Multiple physiological functions for multidrug transporter P-glycoprotein?

Multidrug resistance mediated by the drug-efflux protein P-glycoprotein (P- gp) is one mechanism that tumor cells use to escape death induced by chemot herapeutic drugs. Although it is irrefutable that P-gp can efflux xenobioti cs out of cells, biological regulatory functions for P-gp in multicellular organisms have yet to be established firmly. Recent observations have chall enged the notion that P-gp has evolved merely to efflux xenotoxins out of h ealthy cells and raised the possibility that P-gp and related transporter m olecules might play a fundamental role in regulating cell differentiation, proliferation and survival.